In liquid crystal display manufacturing techniques, a rubbing process is usually adopted to perform a pre-treatment for alignment of liquid crystal molecules. The rubbing process mainly comprises: a substrate coated with a polyimide (PI) film (also known as an alignment film) is placed on a bearing platform; a rubbing-roller wrapped in advance with a rubbing-cloth on its surface is rolled above the bearing platform at a preset rotational speed, thus drives the rubbing-cloth to roll on and across the surface of the alignment film on the substrate with a certain pressure; during the rolling process of the rubbing-cloth, the piles of the surface of the rubbing-cloth interact with the surface of the alignment film, so that grooves are formed on the alignment film. After the completion of the rubbing process, the substrate is cell-assembled with another substrate; and, liquid crystal (LC) molecules are injected between the two substrates. Because anchoring energy exists between the LC molecules and the alignment film, the LC molecules can be aligned in sequence along the grooves, so that the arrangement of the LC molecules within the alignment film meets the requirement of a pretilt angle.
During the rubbing process, the quality of the rubbing effect directly determines the uniformity of the oriental arrangement of liquid crystal molecules, thereby affecting the image display quality of a liquid crystal display. When the surface of the rubbing-cloth has defects, such as unevenness in thickness of the rubbing-cloth, foreign matter adhered to the surface of the rubbing-cloth, and impurities introduced in the weaving and dying processes of the rubbing-cloth, these defects may affect the uniformity of the rubbing-alignment at the corresponding positions, and thereby affecting the alignment properties.
In the prior art, a method for inspecting the quality of a rubbing-cloth is conducted as follows: rubbing an indium-tin oxide (ITO) glass coated with PI, and then using a steam inspection apparatus to perform visual inspection of the rubbing traces on the surface of the ITO glass after rubbing. With such a method, the surface condition of the rubbing-cloth can only be roughly exhibited, and the detected defective points on the rubbing-cloth can not be directly corresponded with the rubbing-cloth, and differences exist in the inspecting results due to different inspectors; moreover it is possible that judgment to the surface condition of the rubbing-cloth is affected due to the surface condition of the ITO glass.